Lexus NX: Catalyst System Efficiency Below Threshold (Bank 1) (P0420)

Lexus NX Service Manual / Engine & Hybrid System / 2ar-fxe (engine Control) / Sfi System / Catalyst System Efficiency Below Threshold (Bank 1) (P0420)

MONITOR DESCRIPTION

The ECM uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency.

The first sensor, the air fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.

In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air fuel ratio control.

The oxygen storage capacity value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air fuel ratio to lean or rich levels. If the cycle of the waveform for the heated oxygen sensor is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor and the oxygen storage capacity of the three-way catalytic converter.

The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. If any deterioration has occurred, the ECM will illuminate the MIL and store a DTC.

This system determines the deterioration of the entire catalyst system (including the front and rear catalysts), by using the oxygen storage capacity value of the front catalyst, that is more sensitive than the rear catalyst, as the representative value. Therefore, be sure to replace the front and rear catalysts together when catalyst replacement is necessary.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0420	Catalyst System Efficiency Below Threshold (Bank 1)	The oxygen storage capacity value is less than the standard value under active air fuel ratio control (1 trip detection logic).	Gas leak from exhaust system Air fuel ratio sensor (sensor 1) Heated oxygen sensor (sensor 2) Exhaust manifold converter sub-assembly (TWC: Front catalyst) and front exhaust pipe assembly (TWC: Rear catalyst) EGR valve assembly	Comes on	DTC stored

CATALYST LOCATION

Exhaust Manifold Converter Sub-assembly

TWC: Front Catalyst

Air Fuel Ratio Sensor (Sensor 1)

Front Exhaust Pipe Assembly

TWC: Rear Catalyst

Heated Oxygen Sensor (Sensor 2)

Center Exhaust Pipe Assembly

Tail Exhaust Pipe Assembly

NOTICE:

If DTC P0420 is output, replace the exhaust manifold converter sub-assembly (*1) and the front exhaust pipe assembly (*3) together when catalyst replacement is necessary (Excluding air fuel ratio sensor*2 and heated oxygen sensor*4).

MONITOR STRATEGY

Related DTCs	P0420: Catalyst deterioration
Required Sensors/Components (Main)	Air fuel ratio sensor Heated oxygen sensor
Required Sensors/Components (Related)	Intake air temperature sensor Mass air flow meter sub-assembly Crankshaft position sensor Engine coolant temperature sensor
Frequency of Operation	Once per driving cycle
Duration	Approximately 30 seconds
MIL Operation	Immediate
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever the following DTCs are not stored	P0010 (Camshaft timing oil control valve) P0011 (VVT system - advance) P0012 (VVT system - retard) P0016 (VVT system - misalignment) P0031, P0032, P101D (Air fuel ratio sensor heater) P0037, P0038, P102D (Heated oxygen sensor heater) P0102, P0103 (Mass air flow meter) P0107, P0108 (Manifold absolute pressure) P0115, P0117, P0118 (Engine coolant temperature sensor) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle position sensor) P0125 (Insufficient coolant temperature for closed loop fuel control) P0136, P0137, P0138, P0139, P013A, P0607 (Heated oxygen sensor) P014C, P014D, P015A, P015B, P2195, P2196, P2237, P2238, P2239, P2252, P2253 (Air fuel ratio sensor) P0171, P0172 (Fuel system) P0300, P0301, P0302, P0303, P0304 (Misfire) P0335 (Crankshaft position sensor) P0340 (Camshaft position sensor) P0340, P0342, P0343 (VVT sensor) P0351, P0352, P0353, P0354 (Igniter) P0401 (EGR system) P219A, P219C, P219D, P219E, P219F (Air-fuel ratio imbalance)
Response rate during fuel cut from rich condition	Completed
Auxiliary battery voltage	11 V or higher
Intake air temperature	-10°C (14°F) or higher
Engine coolant temperature	73°C (163°F) or higher
Atmospheric pressure	76 kPa(abs) [570 mmHg(abs)] or higher
Idling	Off
Engine speed	Less than 4000 rpm
Air fuel ratio sensor status	Activated
Fuel system status	Closed loop
Engine load	10% or higher, and less than 70%
All of the following conditions are met	1, 2 and 3
1. Mass air flow	2.5 gm/sec or more, and less than 50 gm/sec
2. Front catalyst temperature (estimated)	560°C (1040°F) or higher, and less than 770°C (1418°F)
3. Rear catalyst temperature (estimated)	450°C (842°F) or higher, and less than 700°C (1292°F)

TYPICAL MALFUNCTION THRESHOLDS

Oxygen Storage Capacity (OSC) of catalyst (Normalized)

Less than 1

MONITOR RESULT

Refer to detailed information in Checking Monitor Status.

Click here

P0420: Catalyst Efficiency / O2 STORAGE B1

Monitor ID	Test ID	Scaling	Unit	Description
$21	$AF	Multiply by 0.001	No dimension	Oxygen storage capacity of catalyst bank 1 (Normalized)

CONFIRMATION DRIVING PATTERN

HINT:

It is necessary for the response of the heated oxygen sensor to be normal in order to confirm DTC P0420. Therefore, perform the confirmation driving pattern for the heated oxygen sensor monitor before performing the confirmation driving pattern for the catalyst efficiency monitor.
Performing this confirmation driving pattern will activate the catalyst efficiency monitor. This is very useful for verifying the completion of a repair.

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the Techstream on.
Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor.
Check that Catalyst Efficiency / Current is Incomplete.
Put the engine in inspection mode (maintenance mode).
Click here
Start the engine and warm it up until the engine coolant temperature is 73°C (163°F) or higher with the shift lever in P [A].
HINT:

In order to keep the idle stable, turn the A/C and all other electric loads off and do not perform any shift operations.
With the engine running, drive the vehicle at approximately 75 km/h (47 mph) for 10 minutes or more [B].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT:
- Drive the vehicle while keeping the engine load as constant as possible.
- If the engine stops, further depress the accelerator pedal to restart the engine.
With shift state S selected and the engine running, drive the vehicle at 75 km/h (47 mph), and then decelerate the vehicle by releasing the accelerator pedal for 5 seconds or more to perform the fuel-cut [C].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.

HINT:

If the engine stops, further depress the accelerator pedal to restart the engine.
Enter the following menus: Powertrain / Engine and ECT / Monitor / Current Monitor / O2 Sensor / RL F/C B1S2 [D].
Check the Test Value for RL F/C B1S2.
HINT:
- If Test Value displays a value larger than 0, perform the following procedure, as the O2 Sensor monitor is finished.
- If Test Value displays 0, perform step [C] until it displays a value larger than 0, as the O2 Sensor monitor is not finished.
Turn the power switch off and wait for at least 30 seconds [F].
Turn the power switch on (IG) and turn the Techstream on.
Start the engine and warm it up until the engine coolant temperature is 73°C (163°F) or higher [G].
With the engine running, drive the vehicle at approximately 75 km/h (47 mph) for 10 minutes or more [H].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT:
- Drive the vehicle while keeping the engine load as constant as possible.
- The monitor item will change to Complete as the Catalyst Efficiency monitor operates.
- If the engine stops, further depress the accelerator pedal to restart the engine.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [I].
Check if any DTCs are stored.
HINT:

If the monitor item does not change to Complete, and no DTCs are stored, perform the following procedure.
With the engine running, drive the vehicle at approximately 100 km/h (62 mph) for 10 minutes or more [J].
CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT:
- Drive the vehicle while keeping the engine load as constant as possible.
- The monitor item will change to Complete as the Catalyst Efficiency monitor operates.
- If the engine stops, further depress the accelerator pedal to restart the engine.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [K].
Check if any DTCs are stored.
HINT:

If the monitor item does not change to Complete, and no DTCs are stored, extend the driving time.
If no DTC is output, perform a universal trip and check for permanent DTCs.
Click here
HINT:
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.

CONDITIONING FOR SENSOR TESTING

HINT:

Perform the operation with the engine speeds and time durations described below prior to checking the waveforms of the air fuel ratio and heated oxygen sensors. This is to activate the sensors sufficiently to obtain appropriate inspection results.

(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG) and turn the Techstream on [A].
(c) Put the engine in inspection mode (maintenance mode).
Click here
(d) Start the engine and warm it up with all the accessories switched off until the engine coolant temperature stabilizes [B].
(e) Run the engine at an engine speed of 2500 rpm for at least 3 minutes [C].
HINT:

During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, perform step [C] after charging control has completed.
(f) While running the engine at 2500 rpm and 1500 rpm for 2 seconds, check the waveforms of the air fuel ratio and heated oxygen sensors using the Techstream [D].

HINT:

If the voltage output of either the air fuel ratio or heated oxygen sensor does not fluctuate, or there is a noise in the waveform of either sensor, the sensor may be malfunctioning.
If the voltage outputs of both the sensors remain lean or rich, the air fuel ratio may be extremely lean or rich. In such cases, perform the Control the Injection Volume for A/F Sensor Active Test using the Techstream.
If the Three-way Catalytic Converter (TWC) has deteriorated, the heated oxygen sensor (located behind the Three-way Catalytic Converter [TWC]) voltage output fluctuates up and down frequently, even under normal driving conditions (active air fuel ratio control is not performed).

CAUTION / NOTICE / HINT

HINT:

If a malfunction cannot be found when troubleshooting DTC P0420, a lean or rich abnormality may be the cause. Perform troubleshooting by following the inspection procedure for P0171 (System Too Lean), and P0172 (System Too Rich).
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.
Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

PROCEDURE

1.	CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(e) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

Result	Proceed to
DTC P0420 is output	A
DTC P0420 and other DTCs are output	B

HINT:

If any DTCs other than P0420 are output, troubleshoot those DTCs first.

GO TO DTC CHART

2.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine warm it up.

(f) Idle the engine for 5 minutes or more with the shift lever in P.

(g) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Gas AF Control / AFS Voltage B1S1 and O2S B1S2.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the Injection Volume for A/F Sensor

Data List Display
AFS Voltage B1S1
O2S B1S2

(h) Perform the Active Test operation with the engine idling (press the 12.5% or -12.5% button to change the fuel injection volume).

(i) Monitor the voltage outputs of the air fuel ratio sensor and heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

HINT:

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

Standard:

Techstream Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (Air fuel ratio)	12.5%	Rich	Below 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	12.5%	Rich	Higher than 0.55 V
O2S B1S2 (Heated oxygen)	-12.5%	Lean	Below 0.4 V

Status AFS Voltage B1S1	Status O2S B1S2	Actual air fuel ratio, air fuel ratio sensor and heated oxygen sensor condition	Misfire	Main Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	Three-way catalytic converter Gas leak from exhaust system EGR valve assembly	A
Lean	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B
Rich	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B
Lean/Rich	Lean	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leak from exhaust system	C
Lean/Rich	Rich	Heated oxygen sensor malfunction	-	Heated oxygen sensor Gas leak from exhaust system	C
Lean	Lean	Actual air fuel ratio lean	May occur	Extremely lean actual air fuel ratio Gas leak from exhaust system EGR valve assembly	D
Rich	Rich	Actual air fuel ratio rich	-	Extremely rich actual air fuel ratio Gas leak from exhaust system EGR valve assembly	D

Lean: During Control the Injection Volume for A/F Sensor Active Test, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.
Rich: During Control the Injection Volume for A/F Sensor Active Test, AFS Voltage B1S1 is consistently below 3.1 V, and O2S B1S2 is consistently higher than 0.55 V.
Lean/Rich: During Control the Injection Volume for A/F Sensor Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternate correctly.

GO TO STEP 6

GO TO STEP 7

GO TO STEP 9

3.	CHECK FOR EXHAUST GAS LEAK

(a) Check for exhaust gas leaks.

OK:

No gas leaks.

GO TO STEP 13

4.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

The A/C switch and all accessory switches should be off.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Primary / MAP and Throttle Idle Position.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the EGR Step Position

Data List Display
MAP
Throttle Idle Position

(g) Confirm that the Throttle Idle Position is ON and check the MAP values in the Data List while performing the Active Test.

HINT:

Do not leave the EGR valve open for 10 seconds or more during the Active Test.
Be sure to return the EGR valve to step 0 when the Active Test is completed.
Do not open the EGR valve 30 steps or more during the Active Test.

OK:

MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.

Standard:

-	EGR Step Position (Active Test)
0 Steps	0 to 30 Steps
MAP (Data List)	(EGR valve is fully closed)	MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

EGR Step Position (Active Test)

0 Steps

0 to 30 Steps

MAP

(Data List)

(EGR valve is fully closed)

MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

HINT:

While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.
Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

GO TO STEP 15

5.	INSPECT EGR VALVE ASSEMBLY

(a) Remove the EGR valve assembly.

Click here

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly.

Click here

GO TO STEP 15

REPLACE EGR VALVE ASSEMBLY

6.	REPLACE AIR FUEL RATIO SENSOR

(a) Replace the air fuel ratio sensor.

Click here

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

Click here

GO TO STEP 14

7.	CHECK FOR EXHAUST GAS LEAK

(a) Check for exhaust gas leaks.

OK:

No gas leaks.

GO TO STEP 13

8.	REPLACE HEATED OXYGEN SENSOR

(a) Replace the heated oxygen sensor.

Click here

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor.

Click here

GO TO STEP 14

9.	CHECK FOR EXHAUST GAS LEAK

(a) Check for exhaust gas leaks.

OK:

No gas leaks.

GO TO STEP 13

10.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

The A/C switch and all accessory switches should be off.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Primary / MAP and Throttle Idle Position.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the EGR Step Position

Data List Display
MAP
Throttle Idle Position

(g) Confirm that the Throttle Idle Position is ON and check the MAP values in the Data List while performing the Active Test.

HINT:

Do not leave the EGR valve open for 10 seconds or more during the Active Test.
Be sure to return the EGR valve to step 0 when the Active Test is completed.
Do not open the EGR valve 30 steps or more during the Active Test.

OK:

MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.

Standard:

EGR Step Position (Active Test)

0 Steps

0 to 30 Steps

MAP

(Data List)

(EGR valve is fully closed)

MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

HINT:

While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.
Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

GO TO STEP 12

11.	INSPECT EGR VALVE ASSEMBLY

(a) Remove the EGR valve assembly.

Click here

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly.

Click here

REPLACE EGR VALVE ASSEMBLY

12.	CHECK CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO

(a) Check the cause of extremely rich or lean actual air fuel ratio, referring to the DTC P0171 or P0172 Inspection Procedure.

Click here

GO TO STEP 14

13.	REPAIR OR REPLACE EXHAUST GAS LEAK POINT

(a) Repair or replace exhaust gas leak point.

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system.

Click here

14.	CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Clear the DTCs.

Click here

Powertrain > Engine and ECT > Clear DTCs

(e) Turn the power switch off and wait for at least 30 seconds.

(f) Turn the power switch on (IG).

(g) Turn the Techstream on.

(h) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(i) Start the engine.

(j) Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

(k) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(l) Read the pending DTCs.

Powertrain > Engine and ECT > Trouble Codes

Result	Proceed to
DTC P0420 is output	A
DTCs are not output	B

END

15.	REPLACE EXHAUST MANIFOLD CONVERTER SUB-ASSEMBLY (TWC: FRONT CATALYST) AND FRONT EXHAUST PIPE ASSEMBLY (TWC: REAR CATALYST)

NOTICE:

When replacing the exhaust manifold converter sub-assembly (TWC: Front catalyst) and the front exhaust pipe assembly (TWC: Rear catalyst) together when catalyst replacement is necessary.

HINT:

Confirm the replacement parts, referring to the illustration in Catalyst Location.

(a) Replace the exhaust manifold converter sub-assembly (TWC: Front catalyst).

Click here

(b) Replace the front exhaust pipe assembly (TWC: Rear catalyst).

Click here

END

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